The present invention relates to an apparatus for cooling electronic devices and more particularly to thermal connectors adapted for efficiently transferring heat from one printed circuit board (PCB) to another PCB (or housing) without interfering with the convenient removal and replacement of the PCBs.
The relentless quest for performance has driven the clock frequency used in commercially available parts such as microprocessors to values expressed in hundreds of megahertz and in their laboratory counterparts to values expressed in gigahertz. Also, the dramatic increase of the level of integration that has been achieved in recent years, allowing millions of transistors to be positioned on a single piece of semiconductor, results in generated heat that must be dissipated to avoid damaging or destroying electronic devices and to reach higher performance. Such a situation is typically encountered in the field of telecommunications where complex circuitry uses high speed clocks function 24 hours a day, 7 days a week.
Commonly, the provisions made for cooling electronic devices include the use of heat sinks which provide cooling in an air stream. However, since the power consumption of electronic devices increases, the use of active cooling may advantageously replace such air cooling. Such a solution provides better cooling and allows positioning of multiple electronic devices close enough to one another to avoid undesirable long signal path lengths. For example, the use of heat pipes allows the electronic device to be cooled to be moved away from the cooling system. Likewise, the use of heat pipes allows the cooling of several electronic devices with a single central cooling system.
On the other hand, PCBs are well adapted for electrical system evolution to simplify maintenance and other tasks and thus, are a common form of electrical circuit packaging. Today, many electrical systems like computers, routers and switchers are based on a housing containing a backplane comprising active devices and at least one slot to connect a PCB. PCBs are linked to the backplane with connectors, located on the electronic board lower edge and backplane surface, through which signals are transmitted. Since PCBs generally contain active electronic devices, each PCB needs its own cooling system or a shared one. The solution of embedding a cooling system on each PCB leads to several drawbacks. The multiple cooling systems localized on the PCBs are space consuming and, generally, the provided cooling is not efficient when several PCBs are connected close together. When the cooling system is shared between all the connected PCBs, heat must be transferred efficiently from one PCB to another and eventually outside the housing, including without interfering with the convenient removal and replacement of the PCBs.
U.S. Pat. No. 5,343,358 discloses an arrangement for cooling electronic components in a system. Several circuit boards are connected to a backplane electrically and through heat pipes, which are mounted on the boards and provide connections between the electronic components on the boards and the cooling system. The circuit boards, including the attached heat pipes, can be removed from the backplane by detaching electrical connections on the boards from corresponding connectors on the backplane, while at the same time detaching the ends of the heat pipes from sockets in an expander which forms part of the cooling system. If desired, backplanes can be positioned on both sides of the expander, with sockets provided on both sides of the expander to receive end portions of heat pipes.
U.S. Pat. No. 5,946,191 discloses a heat sink structure for an electronic device of the type having a chassis and a plug-in unit, for providing heat dissipation for a heat-generating component on a PCB within the unit as shown on FIG. 1. In a preferred embodiment, a first heat pipe is fixedly attached to a heat dissipating plate for the heat generating component. At the opposite end, the first heat pipe is held by a connector plug attached to the unit. At one end, a second heat pipe is held by a plug-receiving seat that is fixedly attached to a backboard of the chassis. At the opposite end, the second heat pipe is fixedly attached to a heat dissipating portion on the chassis. The first heat pipe, plug, plug-receiving seat and second heat pipe transfer heat from the heat-generating component to the heat-dissipating portion.
In the above mentioned U.S. patents, thermal connection between a PCB and another one or a housing is provided by mechanical pressure using a springy system. Thus, when a PCB is inserted or extracted, a mechanical constraint is exerted on the heat pipes and the efficiency of thermal contacts depends upon the constraint exerted. This could lead to damage the heat pipes or the electrical connectors, in particular when the number of electrical contacts is significant, as in many of today""s switching systems.
It is a primary object of this invention to provide an improved thermal connector for use in electronic assemblies utilizing PCBs.
It is another object of the invention to provide a thermal connector that will provide efficient heat transfer between a first PCB and a heat pipe associated with a second PCB.
It is still another object of the invention to provide such a thermal connector that will function effectively with PCBs that are connectable and separable without interfering with the convenient removal and replacement of such PCBs.
According to one aspect of the invention, there is provided a thermal connector to transfer heat between a first PCB having a device to be cooled thereon and a first heat pipe, and a second PCB having a second heat pipe, the first and second PCBs being connectable and separable, the thermal connector comprising a first part comprised of thermally conductive material attached to the first PCB and thermally connected to the device to be cooled on the first PCB by the first heat pipe, a second part movably positioned relative to the first part so as to occupy a first open position and a second closed position relative thereto, the first and second parts engaging both the first and second heat pipes while the second part occupies the second position so as to provide an effective heat transfer path from the first pipe to the second pipe, and the first and second parts enabling removal of the second pipe while the second part occupies the first position so as to assure facile separation of the first and second heat pipes.
Further advantages of the present invention will become apparent to the ones skilled in the art upon examination of the drawings and detailed description. It is intended that any additional advantages be incorporated herein.